The considerable upsurge in communications by transmission of electronic messages has very quickly raised the problem of the confidentiality of the data transmitted.
Very sophisticated solutions for enciphering/deciphering these data have been proposed by means of encipherment algorithms using a single secret key, serving for encipherment/decipherment, and then a public key, with which is associated a private key, used for deciphering the data, enciphered by means of the public key.
The aforementioned solutions are satisfactory, to the extent that secret-key algorithms are hard to break, at the very least if the secret key is not compromised, and that public-key/private-key algorithms do not entail limitations as regards the dissemination of the public key and require the implementation of hardware and software means of prohibitive complexity and calculation cost with a view either to breaking the encipherment/decipherment algorithm or to retrieving the value of the private key associated with the public key.
In all events, use of a cryptographic scheme with a single secret key or a public key, with which a private key is associated, it is indispensable to prevent any compromising of the secret key or of the private key, so as to guarantee the confidentiality of the data transmitted.
Whilst satisfactory protected-access cryptographic components have been proposed, in particular integrated in the form of security processors for the cryptographic components of electronic cards, termed chip cards, exterior access by way of the input/output port to the security components of these electronic cards possibly being made extremely difficult or indeed practically impossible, the read/write manipulation of the secret or private keys by these components may allow the compromising of the aforementioned keys, in particular of the secret values or secrets entering into the definition of these values.
This compromising may occur through “hidden channel” attack (known as Side Channel attack), this type of attack possibly consisting for example in detecting the intensity variations of the electric current consumed by the security component or the card in the course of these manipulations, these being necessary.
The object of the present invention is to remedy the drawbacks of the risks of hidden channel attack, through the implementation of a method of coding a secret, subdivided into several mutually uncorrelated secret elements, it not being possible for the manipulation of the secret elements to enable the original secret to be retrieved, although each secret element might, as the case may be, be compromised.